WHAT IS MODE HOPPING?

DO DC EXCITED GLASS TUBES EXHIBIT MODE HOPPING?

According to SPT C Series Glass DC Excited Tube documentation, flow rate and temperature can cause mode hoping:

Here is the text of that thread (LINK TO ARTICLE. Look under Attentions):

The flow rate of cooling water should be controlled to 2L-7L/min. Otherwise, the cooling effect is not appropriate, it will cause mode jumps and the power of laser tubes will decrease due to the variation of light spot. The cooling water return port (outlet) must be submerged in the water tank, otherwise the cooling water irrigation in the laser tube will be unsatisfactory every time the laser tube is shut down or turned on. 

cinematic2 posted this in a cnczone.com article asserting the fact that a DC excited tube cannot change modes:

Here is the text of that thread (LINK TO ARTICLE):

1.Because of specific construction all chinese (glass) lasers works in TEM00 mode.
If the output shape is different than round this is not other transverse mode.
This is damage .
2. Typical chinese lasers DO NOT use catalyst.
Recombining is natural process.
3. 15C degree is to low.
It is to close to water condensation edge in specific situation.
4. 40C degree is to high.
At 40C laser will lose about 40-50% power.
Best temperature for chinese lasers is 21-22C.
If you want to have your laser working stable for long time you MUST keep stable temp. 21-22C. No more, no less.
If you want your laser engraving stable quality you MUST keep 21-22C.
So this is why people use professional coolers.

SO WHICH ONE IS IT?

CONTROLLING TEMPERATURE

the water is only present in the center portion of the tube. heating just the ambient air in the tube bay is not a proper solution. the pump and flow sensor in the chiller are made of plastic and they can fail if frozen too. the entire cooling system must be protected from freezing.

teyu chiller (S&A) says there is a heat option available that retrofits on the cw-5000 series. i cannot get info because they handle that on a case by case basis so that would have to go direct through teyu.

others put submersible aquarium heaters in the chiller reservoir